Abstract 1541: Incorporation of an IgG4-derived spacer improves the activity of nanobody-based CAR T cells targeting a membrane-distal epitope of glypican 1 in pancreatic cancer

Abstract

Abstract Background & Aims: Epitope recognition and antigen density have emerged as major parameters affecting the anti-tumor activity of chimeric antigen receptor (CAR) T cells. Glypican 1 (GPC1) is a cell surface proteoglycan that is expressed in pancreatic cancer. Here, we investigate how the choice of an epitope and an extracellular spacer in CAR design can determine T cell activation in high- or low- GPC1-expressing tumors. Methods: We use mouse hybridoma and phage display technologies to isolate GPC1-specific antibodies or nanobodies with distinct epitopes, and analyze GPC1 protein expression in pancreatic cancer. We construct CARs with different extracellular spacers and test them in GPC1-positive cell and mouse models. We use droplet digital PCR and genomic sequencing methods to analyze persistent CAR T cells in mice. Results: We isolate a camel nanobody D4 and a mouse monoclonal antibody HM2 recognizing the membrane-distal and membrane-proximal epitopes of GPC1, respectively, with similar high affinity. GPC1 protein was frequently detected in pancreatic tumor tissues and normal pancreas adjacent to tumors. Both D4 and HM2 CAR T cells with the hinge and transmembrane domain (TM) from CD8 regressed high GPC1-expressing xenograft tumors. Interestingly, D4 CAR containing a short IgG4 hinge spacer and CD28 TM outperformed the initial D4 CAR against low GPC1-expressing tumors in vitro and in vivo. Conclusion: By optimizing spacer and TM designs, the activity of nanobody D4-based CAR T cell targeting a membrane-distal epitope of GPC1 is significantly enhanced against low GPC1-expressing tumors, suggesting it might improve the efficacy of GPC1-targeted CAR T cell therapy in pancreatic cancer. Citation Format: Nan Li, Dan Li, Jiajia Pan, Mitchell Ho. Incorporation of an IgG4-derived spacer improves the activity of nanobody-based CAR T cells targeting a membrane-distal epitope of glypican 1 in pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1541.